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Objective To investigate the generators of the somatosensory evoked potential (SEP) components recorded from the Pedunculopontine Tegmental nucleus (PPTg). Methods Twenty-two patients, suffering from Parkinson’s disease (PD), underwent electrode implantation in the PPTg area for deep brain stimulation (DBS). SEPs were recorded from the DBS electrode contacts to median nerve stimulation. Results SEPs recorded from the PPTg electrode contacts could be classified in 3 types, according to their waveforms. (1) The biphasic potential showed a positive peak (P16) whose latency (16.05 ± 0.61 ms) shifted of 0.18 ± 0.07 ms from the lower to the upper contact of the electrode. (2) The triphasic potential showed an initial positive peak (P15) whose latency (15.4 ± 0.2 ms) did not change across the DBS electrode contacts. (3) In the last SEP configuration (mixed biphasic and triphasic waveform), the positive peak was bifid including both the P15 and P16 potentials. Conclusion While the P16 potential is probably generated by the somatosensory volley travelling along the medial lemniscus, the P15 response represents a far-field potential probably generated at the cuneate nucleus level. Significance Our results show the physiological meaning of the somatosensory responses recorded from the PPTg nucleus area. [ABSTRACT FROM AUTHOR]

The pedunculopontine tegmental nucleus (PPTg) relays basal ganglia signals to the thalamus, lower brainstem and spinal cord. Using the 6-hydroxydopamine (6-OHDA) rat model of parkinsonism, we investigated whether deep brain stimulation (DBS) of the PPTg (40Hz, 60μs, 200-400μA) may influence the preparative and executive phases in a conditioned behavioural task, and the motor asymmetries induced by apomorphine. In the conditioned task, rats had to press two levers according to a fixed delay paradigm. The 6-OHDA lesion was placed in the right medial forebrain bundle, i.e. contralaterally to the preferred forepaw used by rats to press levers in the adopted task. The stimulating electrode was implanted in the right PPTg, i.e. contralateral to left side, which was expected to be most affected. The lesion significantly reduced correct responses from 63.4% to 16.6%. PPTg-DBS effects were episodic; however, when rats successfully performed in the task (18.9%), reaction time (468.8±36.5ms) was significantly increased (589.9±45.9ms), but not improved by PPTg-DBS (646.7±33.8ms). Movement time was significantly increased following the lesion (649.2±42.6ms vs. 810.9±53.0ms), but significantly reduced by PPTg-DBS (820.4±39.4ms) compared to sham PPTg-DBS (979.8±47.6ms). In a second group of lesioned rats, rotations induced by apomorphine were significantly reduced by PPTg-DBS compared to sham PPTg-DBS (12.2±0.6 vs. 9.5±0.4 mean turns/min). Thus, it appears that specific aspects of motor deficits in 6-OHDA-lesioned rats may be modulated by PPTg-DBS. [ABSTRACT FROM AUTHOR]

Abstract: The present paper was aimed at investigating the effect of low-frequency electrical stimulation (25 Hz) of the peduncolopontine (PPN) area on working memory (WM) functioning in patients with Parkinson''s disease (PD). Five PD patients who underwent simultaneous PPN area- and subthalamic nucleus-deep brain stimulation (DBS) implantation participated in the study. PD patients were evaluated in the morning at least 12 h after antiparkinsonian therapy withdrawal in two conditions: i) after continuous PPN area stimulation (Off Therapy/On PPN: “On” condition); ii) at least 120 min after PPN area had been switched “Off” (Off Ther/Off PPN: “Off” condition). The experimental WM task consisted of an n-back paradigm with verbal and visual-object stimuli. PD patients showed a consistent response time decrease on both the verbal and the visual-object tasks passing from the “Off” to the “On” condition (p < 0.05). However, the accuracy score did not significantly differ between the two experimental conditions. The present findings, although preliminary, suggest that PPN area stimulation facilitates the speed processing of information in the content of WM, possibly through the modulation of the attentional resources. [Copyright &y& Elsevier]

Abstract: Combined deep brain stimulation of the subthalamic (STN) and pedunculopontine (PPN) nuclei has been recently proposed as surgical treatment of advanced Parkinson''s disease. STN stimulation alone has been shown to provide selective improvement of the grammatical aspect of language. We studied five advanced Parkinson''s disease patients who underwent combined deep brain stimulation (STN + PPN). Overall cognitive profile did not change. On the contrary, an interesting trend towards reduction of ungrammatical errors (particularly substitution of free and inflectional morphemes) was found when stimulating the STN, and also the PPN, when the STN was switched off. These findings replicate previous observations on the STN, and provide the rationale for further investigation of the role of the PPN in processing linguistic grammar. [Copyright &y& Elsevier]

Abstract: Objective: To investigate whether recording from deep intracerebral (IC) electrodes can disclose laser evoked potential (LEP) components generated under the cerebral cortex. Methods: LEPs were recorded to hand and/or perioral region stimulation from 7 patients suffering from Parkinson’s disease, who underwent implant of IC electrodes in the globus pallidum pars interna (GPi), in the subthalamic nucleus (STN) and in the pedunculopontine nucleus (PPN). LEPs were obtained from the IC electrode contacts and from the Cz vertex, referred to the nose. Results: The scalp traces showed a triphasic response (P1-N2-P2). The IC electrodes recorded two main components (ICP2 and ICN2), showing the same latencies as the scalp N2 and P2 potentials, respectively. The ICP2-ICN2 complex was sometimes preceded by a ICP1 wave at the same latency of the scalp P1 response. Conclusions: The LEP components recorded from the IC electrodes mirrored the ones picked up from the Cz lead, thus suggesting that they are probably generated by the opposite pole of the same cortical sources producing the scalp responses. Significance: In the IC traces, there was no evidence of earlier potentials possibly generated within the thalamus or of subcortical far-field responses. This means that the nociceptive signal amplification occurring within the cerebral cortex is necessary to produce identifiable LEP components. [Copyright &y& Elsevier]

Abstract: The intra-laminar (IL) thalamic complex, composed of centromedian (CM) and parafascicular (Pf) nucleus, is a strategic crossroad for the activity of the basal ganglia and is recently regaining its position has a putative neurosurgical target for Parkinsonian syndromes. The multi-target approach we have encouraged since the late nineties has allowed the combined implantation of a standard target (the subthalamic nucleus—STN or the internal pallidus—GPi) plus an innovative one (CM/Pf) in well-identified Parkinson’s disease (PD) patients; hence, it is possible to study, in the same PD patients, the specific target-mediated effects on different clinical signs. Here, we focus on the potential usefulness of implanting the CM/Pf complex when required in the management of contra-lateral tremor (resistant to standard deep brain stimulation—DBS – in STN – , n =2) and disabling involuntary movements, partially responsive to GPi–DBS (n =6). When considering global UPDRS scores, CM/Pf–DBS ameliorate extra-pyramidal symptoms but not as strongly as STN (or GPi) does. Yet, CM/Pf acts very powerfully on tremor and contributes to the long-term management of l-Dopa-induced involuntary movements. The lack of cognitive deficits and psychic impairment associated with the improvement of their quality of life, in our small cohort of CM/Pf implanted patients, reinforces the notion of CM/Pf as a safe and attractive area for surgical treatment of advanced PD, possibly affecting not only motor but also associative functions. [Copyright &y& Elsevier]